Hepatitis C virus (HCV) is a leading cause of chronic hepatitis and hepatocellular carcinoma worldwide and infects more than 1% of the world's population. Successful vaccine development is pivotal in controlling this global health problem. A system for efficient assembly of HCV structural proteins into HCV-like particles (VLPs) in insect cells has been developed in our laboratory. These non-infectious HCV-like particles had similar morphologic, serologic and biophysical properties as the putative virions isolated from HCV infected humans. In contrast to recombinant subunit vaccines, the viral proteins of HCV-like particles are presented in a native, virion-like conformation and may therefore be superior in eliciting a protective humoral and cellular immune response. These VLPs elicited high titers of antibodies against HCV in animals. Because of the particular nature of the antigen, cytotoxic T cell responses, which have been shown to be important in controlling viral infection, may also be induced. Experiments are under way to analyze this aspect of immune response in mice. Studies have also been extended to full-length HCV cDNA. A full-length HCV genome was assembled from overlapping cDNA clones. HCV polyprotein was expressed from the recombinant baculovirus with correct processing to yield all the structural and nonstructural HCV proteins at high levels. Experiments are currently underway to determine whether virus-like particles are produced in insect cells and whether the full-length HCV construct is able to replicate and generate infectious virions in this system. These work will not only facilitate studies into HCV replication but also may provide a tissue culture-based system for generation of candidate vaccines and screening of potential antiviral agents.